The present invention relates to a method and system for performing an automatic answering function, and more particularly, to a method and system for rapidly recognizing various busy tone patterns used in different countries.
Conventionally, an automatic answering function is performed when an incoming call from a calling party is received by a telephone answering system during a user's absence. In response to the incoming call, a pre-recorded greeting message from the user is transmitted to the calling party under the control of the telephone answering system. A message received from the calling party is then recorded, and upon the request of the user, the message received from the calling party is reproduced for the user. Such an automatic answering function has facilitated user convenience by being used in terminals of wired and wireless telephone sets and facsimile machines.
In implementing the automatic answering function, it is important how fast the automatic answering system detects when the calling party has terminated the call by hanging up the handset of his telephone. After the system detects that the calling party has terminated the call, the operation of recording signals on a recording medium of the system is stopped.
Once the calling party terminates the call by hanging up the handset of his telephone, most exchange systems transmit a busy tone to the answering system. Therefore, the answering system recognizes that the calling party has terminated the call by detecting the busy tone. Typically, the answering system continues to record signals onto the recording medium until the busy tone is detected. According to this conventional method, the recording operation is stopped about 12 seconds after the calling party's message has been completed. In other words, the time period necessary for the automatic answering system to detect the busy tone is about 12 seconds. In this situation, there is a problem in that the busy tone, or silence, is unnecessarily recorded on the recording medium of the answering system.
To solve this problem, the unnecessary recorded portion, for example, about 6 seconds before the recording is stopped, can be erased. This solution, however, has a defect in that it requires the user to inconveniently erase the unnecessary portion of the recorded message which is usually very difficult to accurately locate.
Generally, busy tones are classified according to pulse width pattern. Different countries and exchanges use busy tones having different pulse width patterns. Therefore, the automatic answering system often requires a long period of time (i.e., about 12 seconds) to detect the busy tone used by a particular exchange or country since the system possesses no information regarding the pulse width pattern of the busy tone. As a result, the automatic answering system must record unnecessary information on the recording medium, thereby making it difficult to efficiently use the recording medium. However, if the automatic answering system is able to recognize the pattern of the busy tone used by the particular exchange or country, the busy tone can be detected in about 6 seconds.
From the discussion above, it can be appreciated that a preferable solution for eliminating unnecessary recording is to accurately detect the busy tone within a minimum period of time.
One prior art reference that seeks to detect a busy tone is disclosed in U.S. Pat. No. 4,694,482 entitled Digital Tone Detector issued to Reesor et al. In Reesor et al. '482, a digital tone detector generates one or more reference tones having user definable frequencies, and performs single frequency discrete Fourier transforms on one or more signals received from the telephone line at the defined frequencies to provide an indication of whether or not one or more predetermined busy tones frequencies are detected in the received signals. While conventional art, such as Reesor et al. '482, possesses merit in its own right, I believe that an improved method for accurately detecting a busy tone within minimum period of time can be contemplated.